1. Field of the Invention
The present invention relates generally to a projector type lighting device such as a fog lamp or the like employable for a vehicle. More particularly, the present invention relates to improvement of a projector type lighting device of the foregoing type of which light beam utilizing rate is improved, and moreover, of which light irradiating intensity is substantially increased.
2. Background Art
To facilitate understanding of the present invention, a typical conventional projector type lighting device of the foregoing type will briefly be described below with reference to FIG. 5.
As shown in FIG. 5, a conventional projector type lighting device (hereinafter referred to simply as a lighting device) 90 includes a light source 92 of which lamp filament is located at one focus f of a reflective mirror 91 having a revolving parabolic surface, a composite parabolic surface of the like. In addition, the lighting device 90 includes a projecting lens 93 at the foremost end thereof. As light is generated from the light source 92 and then reflected at the reflective mirror 91, the reflected light is emitted toward the other focus of the reflective mirror 91 at which it converges in the form of a light beam having a substantially circular sectional shape. Since a shading plate 94 is interposed between the reflective mirror 91 and the projecting lens 93, the resultant light beam having a sectional shape corresponding to a semicircle having a lower arc does not contain any upward orienting light component but the lighting device 90 exhibits light distribution properties preferably employable for a light beam to be emitted to a vehicle running in the opposite direction to pass by a vehicle having the lighting device 90 mounted thereon.
With the conventional lighting device 90 constructed in the above-described manner, since all the substantially half of light beam reflected from the reflective mirror 91 is covered with the shading plate 94 to provide the lighting device 90 with the foregoing light distribution properties, a first problem is that a light beam utilizing rate of the light source 92 is reduced to a level of about 50%, resulting in a high degree of illumination corresponding to the quantity of electricity consumed by the light source 92 failing to be obtained with the lighting device 90.
In addition, since light is hardly irradiated to the region located outside of the range defined by the reflective mirror 91, a second problem is that e.g., a road shoulder part located outside of the foregoing range is not illuminated with the light beam emitted from the lighting device 90, and moreover, a person walking ahead of the vehicle in the vicinity of the same is hardly visually recognized by a driver sitting on his seat in the vehicle.